CAD improves surgical devices

Laproscopic techniques have eliminated many of the more traumatic aspects of surgery. The ability of doctors to explore the abdominal cavity with a CCD camera inserted through a small incision, and even to administer treatment through these same incisions, has reduced patient recovery time, hospital stays, and expense.

The success of today's laproscopic surgery depends in large part on a new generation of medical devices developed to support surgeons. To develop and integrate the combination of unique and off-the-shelf components these devices require, designers increasingly turn to solid-modeling CAD systems. Among engineers in the forefront of medical device design, CAD is widely regarded as essential for creating geometry, packaging components, and streamlining time to market--and thence to physicians' hands.

A leader in laproscopic medical devices is Davol Inc. (Cranston, RI), a division of C.R. Bard, Inc. According to Roger Darois, director of product development, one of the hallmarks of his company's position in the field is its ability to offer a complete line of surgical instruments for a wide variety of procedures. "Davol has been developing tools for laproscopy since the procedure's inception in the early 1980s," Darois says. "These days, competition forces us to stay on top of those technologies that help get the best quality products to market fastest."

In good hands. Darois emphasizes the role CAD--and solid modeling in particular--plays in achieving this goal. With Davol's battery-powered laproscopic irrigation unit, solid modeling was used extensively throughout the development cycle for engineering, proof of concept, marketing, and even FDA certification purposes.

Irrigation devices are used by laproscopic surgeons to flush debris and clean wounds to reveal bleeders. These functions are particularly important during laproscopic procedures due to the restricted access and visibility in the abdominal cavity. A battery-operated device offers advantages of portability, ease of set-up, and ease of disposal.

Davol sought help from Item New Product Development, Providence, RI, a firm specializing in concept-through-manufacturing engineering and industrial design services. "Very early in the conceptual design phase, we and Davol agreed the battery-powered unit should be disposable," reports Marco Wo, senior designer at Item. Such an irrigation system would be more sterile than re-usable units and more cost-effective in the long run. "However, disposability imposes new design challenges, in that ease of disassembly and component cost issues assumed greater importance."

Item's engineers and designers made robust use of their CAD system, MicroStation Modeler from Bentley Systems Inc. (Exton, PA) running on Alpha NT workstations from Digital Equipment Corp. (Maynard, MA), to solve these problems and hasten product development. The key, says Wo, is to do as much of the design work in solids as possible. Solid modeling geometry, he adds, can be applied to nearly every aspect of product development. This helped propel the unit from concept to market in seven months, a major achievement even for the time-sensitive medical device industry.

"Only in 3-D do you see the real impact of your concepts," Wo says. "2-D sketches and drawings can be misleading at times."

Impelling design. The battery-powered laproscopic irrigation system incorporates four basic sections: a pump that includes an integral spike for insertion into the IV bag or bottle (typically containing saline, al-though other solutions are used), a fluid chamber and impeller, an electric motor, and batteries to drive it; tubing connecting the pump to the hand-piece; the hand-piece itself; and a tip selected by the surgeon for a particular application. Only the pump assembly for the new Davol unit had to be designed from scratch. Modifications were made to existing hand-piece designs to incorporate a remote on/off switch, to conserve battery power during longer operations.

The "guts" of the pump assembly are tightly packaged within the acrylic exterior. Wo says solid models are important for ensuring that everything fits and that disassembly will not pose a problem. In order to dispose of the unit safely, the batteries have to be removed first.Item designers developed a snap-like fastener to hold the unit together securely during use. Afterward, the snap is depressed with a tool, such as a screwdriver, facilitating battery removal and separate disposal.

Chief among the new components required for the project was the impeller used to draw solution from the IV reservoir. The impeller, produced by plastic injection-molding, features many contoured shapes and curved surfaces. Solid modeling made creating the complex geometry and the mold design much easier, says Wo.

Another benefit of solid modeling: the components, once modeled, could be converted into SLA files for producing rapid prototypes with stereolithography. Darois says the project was the first time his company had employed SLA models for testing, and that the technique was instrumental in receiving FDA certification of what became the Hydro-Surg® in a timely way.

Other applications

Disposable battery-operated devices

Portable pumping devices

Delivering fluids to inaccessible locations

Using the Hydro-Surg

..The Hydro-Surg laproscopic irrigation system is packaged as a sterile kit. After the components are unwrapped and inspected, assembly and use are straightforward:

Connect the pump spike to the irrigation bag, ensuring the spike is at least one foot above the patient's height.

Connect suction tubing to the suction source.

Attach selected probe tip to trumpet valve and make sure it is fully sealed.

Activate the irrigation probe via the blue-marked button and gravity prime until all air is out of the system.

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